This invention relates to an automated pipetting system and, particularly, to a system with multiple pipetting probes which have individual positioning and individual metering controls.
Conventional automated pipetting systems are used to perform repetitive laboratory mixing, sampling or transferring of fluids in multiwell plates or multiple sets of vials or test tubes. Generally, one or more probes having fluid carrying tips are manipulated over an array of tubes by an arm which is robotically driven in three dimensions (X, Y, Z axes) to carry out programmed procedures under control of an associated computer. Desired procedures include dropping measured quantities of fluid from the tips into the tubes, taking fluid samples from the tubes into the tips, delivering measured quantities into fluids in the tubes at specified depths, prewetting the probes' tips, blowing out the tips to clear them, touching the tips to samples or a cleaning surface and changing the tips.
However, conventional pipetting systems have a number of limitations. Many systems have only one probe with one tip. Some systems have changeable pipette heads with multiple tips in parallel, but all tips are controlled together so that each one dispenses the same amount as the others. A few systems have independently dispensing probes, but they are not independently driven in the Z-xis (vertical) direction because the space taken up by the probe drive mechanisms would not fit the desired tight spacing of the plate wells or test tube array. Therefore, such systems can only drive all the probe tips together to the same depth in the wells or tubes. The smallest quantity which conventional probes can accurately dispense is usually of the order of 10 microliters. Since the probe or probes are usually mounted on a carriage movable along a cantilevered arm, these systems have the problem that the tips cannot be positioned with a high degree of precision due to mechanical bending or bowing or to misalignment.